Method and Apparatus for Integrated Circuit Mask Patterning

ABSTRACT

Provided is an integrated circuit (IC) design method. The method includes receiving a design layout of the IC, the design layout having a first main feature, and adding a negative assist feature to the design layout, wherein the negative assist feature has a first width, the negative assist feature divides the first main feature into a second main feature and a third main feature by the first width, and the first width is sub-resolution in a photolithography process.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. In the course of IC evolution, functional density (i.e., thenumber of interconnected devices per chip area) has generally increasedwhile geometry size (i.e., the smallest component (or line) that can becreated using a fabrication process) has decreased. This scaling downprocess generally provides benefits by increasing production efficiencyand lowering associated costs. Such scaling down has also increased thecomplexity of processing and manufacturing ICs and, for these advancesto be realized, similar developments in IC manufacturing are needed.

For example, as IC technologies are continually progressing to smallertechnology nodes, such as a 65 nm technology node, a 45 nm technologynode, and below, simply scaling down similar designs used at largernodes often results in inaccurate or poorly shaped device features.Rounded corners on a device feature that is designed to have right-anglecorners may become more pronounced or more critical in the smallernodes, preventing the device from performing as desired. Other examplesof inaccurate or poorly shaped device features include pinching,necking, bridging, dishing, erosion, metal line thickness variations,and other characteristics that affect device performance. Typically,optical proximity correction (OPC) may be performed on a design patternto help alleviate some of these difficulties before the pattern iscreated on a mask. However, current OPC techniques may not offer enoughfidelity to correct problems in sub-45 nm designs. Improvements in thisarea are desired.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 is a simplified block diagram of an embodiment of an integratedcircuit (IC) manufacturing system and an associated IC manufacturingflow.

FIG. 2 is a more detailed block diagram of the mask house shown in FIG.1 according to various aspects of the present disclosure.

FIG. 3 is a high-level flowchart of a method of modifying an IC designlayout before mask fabrication according to various aspects of thepresent disclosure.

FIGS. 4A-4D illustrate an IC feature mask creation according to variousaspects of the present disclosure.

FIGS. 5A-5C illustrate another IC feature mask creation according tovarious aspects of the present disclosure.

FIGS. 6A-6C illustrate various IC feature mask creation according tovarious aspects of the present disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the disclosure. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.Moreover, the performance of a first process before a second process inthe description that follows may include embodiments in which the secondprocess is performed immediately after the first process, and may alsoinclude embodiments in which additional processes may be performedbetween the first and second processes. Various features may bearbitrarily drawn in different scales for the sake of simplicity andclarity. Furthermore, the formation of a first feature over or on asecond feature in the description that follows may include embodimentsin which the first and second features are formed in direct contact, andmay also include embodiments in which additional features may be formedbetween the first and second features, such that the first and secondfeatures may not be in direct contact.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. For example, if the device in the figures is turned over,elements described as being “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the exemplary term “below” can encompass both an orientation ofabove and below. The apparatus may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein may likewise be interpreted accordingly.

FIG. 1 is a simplified block diagram of an embodiment of an integratedcircuit (IC) manufacturing system 100 and an IC manufacturing flowassociated with the IC manufacturing system. The IC manufacturing system100 includes a plurality of entities, such as a design house 120, a maskhouse 130, and an IC manufacturer 150 (i.e., a fab), that interact withone another in the design, development, and manufacturing cycles and/orservices related to manufacturing an integrated circuit (IC) device 160.The plurality of entities are connected by a communications network,which may be a single network or a variety of different networks, suchas an intranet and the Internet, and may include wired and/or wirelesscommunication channels. Each entity may interact with other entities andmay provide services to and/or receive services from the other entities.One or more of the design house 120, mask house 130, and IC manufacturer150 may be owned by a single larger company, and may even coexist in acommon facility and use common resources.

The design house (or design team) 120 generates an IC design layout 122.The IC design layout 122 includes various geometrical patterns designedfor an IC product, based on a specification of the IC product to bemanufactured. The geometrical patterns correspond to patterns of metal,oxide, or semiconductor layers that make up the various components ofthe IC device 160 to be fabricated. The various layers combine to formvarious IC features. For example, a portion of the IC design layout 122includes various IC features, such as an active region, gate electrode,source and drain, metal lines or vias of an interlayer interconnection,and openings for bonding pads, to be formed in a semiconductor substrate(such as a silicon wafer) and various material layers disposed on thesemiconductor substrate. The design house 120 implements a proper designprocedure to form the IC design layout 122. The design procedure mayinclude logic design, physical design, and/or place and route. The ICdesign layout 122 is presented in one or more data files havinginformation of the geometrical patterns. For example, the IC designlayout 122 can be expressed in a GDSII file format or DFII file format.

The mask house 130 uses the IC design layout 122 to manufacture one ormore masks to be used for fabricating the various layers of the ICdevice 160 according to the IC design layout 122. The mask house 130performs mask data preparation 132, where the IC design layout 122 istranslated into a form that can be physically written by a mask writer,and mask fabrication 144, where the design layout prepared by the maskdata preparation 132 is modified to comply with a particular mask writerand/or mask manufacturer and is then fabricated. In the presentembodiment, the mask data preparation 132 and mask fabrication 144 areillustrated as separate elements, however, the mask data preparation 132and mask fabrication 144 can be collectively referred to as mask datapreparation.

The mask data preparation 132 includes an optical proximity correction(OPC) 136, a mask rule checker (MRC) 138 and a lithography processchecker (LPC) 140. OPC 136 uses lithography enhancement techniques tocompensate for image errors, such as those that can arise fromdiffraction, interference, or other process effects. OPC 136 may addassist features, such as scattering bars, serif, and/or hammerheads tothe IC design layout 122 according to optical models or rules such that,after a lithography process, a final pattern on a wafer is improved withenhanced resolution and precision. Optical proximity correctionaccording to the illustrated embodiment will be described in greaterdetail below. The mask data preparation 132 can include furtherresolution enhancement techniques, such as off-axis illumination,sub-resolution assist features, phase-shifting masks, other suitabletechniques, or combinations thereof.

MRC 138 checks the IC design layout that has undergone processes in OPC136 with a set of mask creation rules which may contain certaingeometric and connectivity restrictions to ensure sufficient margins, toaccount for variability in semiconductor manufacturing processes. MRC138 modifies the IC design layout to compensate for limitations duringmask fabrication 144. In some scenarios, MRC 138 may undo part of themodifications performed by OPC 136 in order to meet mask creation rules.Consequently, resultant IC masks may not produce desirable IC featureson a wafer. Enhancements in OPC 136 and MRC 138 processes according tovarious aspects of the present disclosure will be described in greaterdetails below.

LPC 140 simulates processing that will be implemented by the ICmanufacturer 150 to fabricate the IC device 160. LPC 140 simulates thisprocessing based on the IC design layout 122 to create a simulatedmanufactured device, such as the IC device 160. In one embodiment, LPC140 determines what shape a hypothetical photomask having a feature thusmodified by OPC 136 and MRC 138 would produce on a wafer if thephotomask was exposed by a photolithography tool described by the LPCmodels (or rules) 142. A simulated shape is called a contour. Thesimulated manufactured device includes simulated contours of all or aportion of the IC design layout. The LPC models (or rules) 142 may bebased on actual processing parameters of the IC manufacturer 150. Theprocessing parameters can include parameters associated with variousprocesses of the IC manufacturing cycle, parameters associated withtools used for manufacturing the IC, and/or other aspects of themanufacturing process. LPC 140 takes into account various factors, suchas aerial image contrast, depth of focus (“DOF”), mask error sensitivity(“MEEF”), other suitable factors, or combinations thereof.

After a simulated manufactured device has been created by LPC 140, ifthe simulated device is not close enough in shape to satisfy designrules, certain steps in the mask data preparation 132, such as OPC 136and MRC 138, may be repeated to refine the IC design layout 122 further.

It should be understood that the above description of the mask datapreparation 132 has been simplified for the purposes of clarity, anddata preparation may include additional features such as a logicoperation (LOP) to modify the IC design layout according tomanufacturing rules, a retarget process (RET) to modify the IC designlayout to compensate for limitations in lithographic processes used byIC manufacturer 150. Additionally, the processes applied to the ICdesign layout 122 during data preparation 132 may be executed in avariety of different orders.

After mask data preparation 132 and during mask fabrication 144, a maskor a group of masks are fabricated based on the modified IC designlayout. For example, an electron-beam (e-beam) or a mechanism ofmultiple e-beams is used to form a pattern on a mask (photomask orreticle) based on the modified IC design layout. The mask can be formedin various technologies. In one embodiment, the mask is formed usingbinary technology. In the present embodiment, a mask pattern includesopaque regions and transparent regions. A radiation beam, such as anultraviolet (UV) beam, used to expose the image sensitive material layer(e.g., photoresist) coated on a wafer, is blocked by the opaque regionand transmits through the transparent regions. In one example, a binarymask includes a transparent substrate (e.g., fused quartz) and an opaquematerial (e.g., chromium) coated in the opaque regions of the mask. Inanother example, the mask is formed using a phase shift technology. Inthe phase shift mask (PSM), various features in the pattern formed onthe mask are configured to have proper phase difference to enhance theresolution and imaging quality. In various examples, the phase shiftmask can be attenuated PSM or alternating PSM as known in the art.

The IC manufacturer 150, such as a semiconductor foundry, uses the mask(or masks) fabricated by the mask house 130 to fabricate the IC device160. The IC manufacturer 150 is a IC fabrication business that caninclude a myriad of manufacturing facilities for the fabrication of avariety of different IC products. For example, there may be amanufacturing facility for the front end fabrication of a plurality ofIC products (i.e., front-end-of-line (FEOL) fabrication), while a secondmanufacturing facility may provide the back end fabrication for theinterconnection and packaging of the IC products (i.e., back-end-of-line(BEOL) fabrication), and a third manufacturing facility may provideother services for the foundry business. In the present embodiment, asemiconductor wafer is fabricated using the mask (or masks) to form theIC device 160. The semiconductor wafer includes a silicon substrate orother proper substrate having material layers formed thereon. Otherproper substrate materials include another suitable elementarysemiconductor, such as diamond or germanium; a suitable compoundsemiconductor, such as silicon carbide, indium arsenide, or indiumphosphide; or a suitable alloy semiconductor, such as silicon germaniumcarbide, gallium arsenic phosphide, or gallium indium phosphide. Thesemiconductor wafer may further include various doped regions,dielectric features, and multilevel interconnects (formed at subsequentmanufacturing steps). The mask may be used in a variety of processes.For example, the mask may be used in an ion implantation process to formvarious doped regions in the semiconductor wafer, in an etching processto form various etching regions in the semiconductor wafer, and/or othersuitable processes.

FIG. 2 is a more detailed block diagram of the mask house 130 shown inFIG. 1 according to various aspects of the present disclosure. In theillustrated embodiment, the mask house 130 includes a mask design system180 that is operable to perform the functionality described inassociation with mask data preparation 132 of FIG. 1. The mask designsystem 180 is an information handling system such as a computer, server,workstation, or other suitable device. The system 180 includes aprocessor 182 that is communicatively coupled to a system memory 184, amass storage device 186, and a communication module 188. The systemmemory 184 provides the processor 182 with non-transitory,computer-readable storage to facilitate execution of computerinstructions by the processor. Examples of system memory may includerandom access memory (RAM) devices such as dynamic RAM (DRAM),synchronous DRAM (SDRAM), solid state memory devices, and/or a varietyof other memory devices known in the art. Computer programs,instructions, and data are stored on the mass storage device 186.Examples of mass storage devices may include hard discs, optical disks,magneto-optical discs, solid-state storage devices, and/or a varietyother mass storage devices known in the art. The communication module188 is operable to communicate information such as IC design layoutfiles with the other components in the IC manufacturing system 100, suchas design house 120. Examples of communication modules may includeEthernet cards, 802.11 WiFi devices, cellular data radios, and/or othersuitable devices known in the art.

In operation, the mask design system 180 is configured to manipulate theIC design layout 122 according to a variety of design rules andlimitations before it is transferred to a mask 190 by mask fabrication144. For example, in one embodiment, OPC 136, MRC 138 and LPC 140 may beimplemented as software instructions executing on the mask design system180. In such an embodiment, the mask design system 180 receives a firstGDSII file 192 containing the IC design layout 122 from the design house120. After the mask data preparation 132 is complete, the mask designsystem 180 transmits a second GDSII file 194 containing a modified ICdesign layout to mask fabrication 144. In alternative embodiments, theIC design layout may be transmitted between the components in ICmanufacturing system 100 in alternate file formats such as DFII, CIF,OASIS, or any other suitable file type. Further, the mask design system180 and the mask house 130 may include additional and/or differentcomponents in alternative embodiments.

FIG. 3 is a high-level flowchart of a method 300 of modifying an ICdesign layout before mask fabrication according to various aspects ofthe present disclosure. In one embodiment, the method 300 may beimplemented in the mask data preparation 132 of mask house 130 shown inFIG. 1. Further, the method 300 in FIG. 3 is a high-level overview anddetails associated with each operation in the method will be describedin association with the subsequent figures in the present disclosure.

The method 300 begins at operation 302 where the mask house 130 receivesthe IC design layout 122. The IC design layout 122 includes variousgeometrical patterns representing features of an integrated circuit. Forexample, the IC design layout 122 may include main IC features such asactive regions, gate electrodes, sources and drains, metal lines,interlayer interconnection vias, and openings for bonding pads that maybe formed in a semiconductor substrate (such as a silicon wafer) andvarious material layers disposed over the semiconductor substrate. TheIC design layout 122 may also include certain assist features, such asthose features for imaging effect, processing enhancement, and/or maskidentification information.

In this regard, FIG. 4A illustrates an example IC feature 400 that is afeature contained in the IC design layout 122. The IC feature 400 mayalso be viewed as a sub-feature 400 a connected with a sub-feature 400 bby a sub IC feature 400 c. Ideally, when the IC feature 400 is formed onthe integrated circuit 160, it will maintain the same shape, but this isnot always so due to limitations in various manufacturing processes.

The method 300 (FIG. 3) proceeds to operation 306 where an assistfeature 414, having a width W1 and a length W2, is added to the ICfeature 400. Further reference is made to FIG. 4B. The assist feature414 meets mask creation rules. It is thus referred to as an MRC cleanassist feature. In the present embodiment, the assist feature 414 has aneffect of blocking a part of the IC feature 400 from being formed on themask 190. Moreover, the assist feature 414 itself will not be formed onthe mask 190. Such assist feature is referred to as a negative assistfeature. In the present embodiment, the assist feature 414 is thusreferred to as an MRC clean negative assist feature. As a result ofadding the assist feature 414, the IC feature 400 is divided into twofeatures, 410 a and 410 b, as illustrated in FIG. 4B, for remainingoperations in the method 300. From an alternative point of view, theeffect of adding the assist feature 414 is to remove part of the ICfeature 400 c thus disconnecting the IC feature 400 a from the ICfeature 400 b. In other embodiments of present disclosure, an MRC cleanassist feature is added to a design layout such that multiple ICfeatures are thus connected by the MRC clean assist feature to form oneIC feature for remaining operations in the method 300. Such MRC cleanassist feature is thus referred to as an MRC clean positive assistfeature. An MRC clean positive assist feature itself is also formed onthe mask 190 as a sub-resolution feature. In another word, it does notbecome part of an IC device on a wafer.

The method 300 next proceeds to operation 310 where an optical proximitycorrection, such as OPC 136, is performed on the IC design layout 122 asmodified in operation 306. In general, OPC is utilized to modify theshape of an IC feature to compensate for diffraction or other processeffects so that the shape of the feature as formed in the finalintegrated circuit closely matches the shape of the feature in the ICdesign layout.

Referring now to FIG. 4C, in the present embodiment, OPC 136 isperformed on the features 410 a and 410 b to generate two modifiedfeatures 420 a and 420 b respectively. In one embodiment, OPC 136includes an iterative process where at least part of an IC featureboundary is modified and thereafter a simulation is performed togenerate contours. Such process repeats until the simulated contoursmeet a target boundary. In the present embodiment as illustrated in FIG.4C, parts of boundaries of the features 410 a and 410 b are modifiedsuch that contours 426 and 428 meet a target boundary as defined by anouter boundary of the IC feature 400, and the features 410 a and 410 bthus modified have become the features 420 a and 420 b respectively.

The method 300 next proceeds to operation 320 where the IC design layoutas modified by operation 310 is checked against various mask creationrules. In the present embodiment, various dimensions of the features 420a and 420 b are checked, including dimensions W4 a, W5 a, W4 b and W5 b,as shown in FIG. 4C. In the present embodiment, various spacing betweenthe features 420 a and 420 b are also checked, including spacing W6 asshown in FIG. 4C. The various dimensions and spacing may be adjusted tomeet mask creation rules. One rule on the spacing W6 is that it is asub-resolution spacing during IC fabrication. In another word, when anIC is fabricated with a mask having the features 420 a and 420 b, the ICwill contain one IC feature 430, as shown in FIG. 4D, and will notcontain spacing W6.

The method 300 proceeds to operation 330 where a photolithographysimulation, such as LPC 140 is performed on the design layout togenerate simulated contours. In that regard, FIG. 4D illustrates examplecontours 436 and 438 that result from the photolithography simulationperformed in operation 330 upon features 420 a and 420 b.

Next, the method 300 proceeds to operation 340 where simulated contoursare compared to a target boundary along the IC feature 400. Thisoperation is sometimes called an OPC evaluation. Specifically, it isdetermined whether the simulated contours meet or overlap the targetboundary. If the simulated contours pass the OPC evaluation, then themethod 300 finishes at operation 350 where the IC design layout havingthe features 420 a and 420 b is saved to the GDSII file 194 andtransferred to mask fabrication 144, where the IC design layout isformed on the photomask 190. If the simulated contours do not pass theOPC evaluation, the method 300 proceeds instead to operation 360, wherelocations of the MRC clean assist features as well as various dimensionsof MRC clean assist features are adjusted. Referring to FIG. 4B, in thepresent embodiment, dimensions W1 and W2 of the assist feature 414 maybe adjusted while maintaining the assist feature 414 being MRC clean.Also in the present embodiment, the assist feature 414 may be movedwithin the sub-feature 400 c while it still divides the IC feature 400to two features. Thereafter, OPC steps described above are begun againto enhance the fidelity of the contours.

It is understood that the method of modifying an IC design layout beforemask fabrication of the illustrated embodiment is simply an example andin alternative embodiments, additional and/or different steps may beincluded in the method. Further, the IC feature illustrated herein maybe substituted for any number of different IC features, and theoperations of method 300 may be applied to the different IC features ina similar manner. In one embodiment, after receiving an IC design layoutin operation 302, an initial lithography process simulation of the ICdesign layout is performed to identify candidate IC features foroperation 306. For example, a candidate IC feature is one havingsimulated contours off a target boundary as defined by an outer boundaryof the IC feature.

Further, as illustrated above in FIGS. 4A-4D, the MRC clean negativeassist feature 414 added in operation 306 has an effect of separatingthe IC feature 400 to multiple features with sub-resolution spacing forOPC 136 purposes. It thus increases the number of polygons in a designlayout. In another embodiment, an MRC clean positive assist featureadded in operation 306 may have an effect of connecting multiple ICfeatures into one IC feature for OPC 136 purposes, thus reducing thenumber of polygons in a design layout. One example of using such an MRCclean positive assist feature is illustrated in FIGS. 5A-5C. FIG. 5Ashows an IC design layout having two IC features, 500 and 502. The twoIC features 500 and 502 are so spaced that an OPC is to be performed tothe two IC features. FIG. 5B shows that an MRC clean positive assistfeature 514 is added to the design layout, connecting the IC features500 and 502. FIG. 6C shows that, OPC 136 modifies outer boundaries of ICfeatures 500 and 502 for correcting optical proximity effect, resultingin modified IC features 520 and 522 respectively. Also shown in FIG. 5Cis a sub-resolution feature 524, resulted from the MRC clean positiveassist feature 514.

More examples of using MRC clean positive assist features for OPCpurposes are illustrated in FIGS. 6A-6C. FIG. 6A shows MRC cleanpositive assist features, 612, 614 and 616, connecting main IC featureshead-to-head. FIG. 6B shows MRC clean positive assist features 622, 624,626 and 628, connecting main IC features side-by-side. FIG. 6C shows MRCclean positive assist features, 632, 634, 636, 642, 644, 646 and 648,connecting main IC features head-to-head and side-by-side.

Further, the method 300 of modifying an IC design layout before maskfabrication of the illustrated embodiment is designed to be executed onany computing architecture, such as the mask design system 180 describedin association with FIG. 2. For example, the method 300 may be executedon a single computer, local area networks, client-server networks, widearea networks, internets, hand-held and other portable and wirelessdevices and networks. Such architecture can take the form of an entirelyhardware embodiment, an entirely software embodiment, or an embodimentcontaining both hardware and software elements. Hardware generallyincludes at least processor-capable platforms, such as client-machines(also known as personal computers or servers), and hand-held processingdevices (such as smart phones, personal digital assistants (PDAs), orpersonal computing devices (PCDs), for example. Hardware can include anyphysical device that is capable of storing machine-readableinstructions, such as memory or other data storage devices. Other formsof hardware include hardware sub-systems, including transfer devicessuch as modems, modem cards, ports, and port cards, for example.Software generally includes any machine code stored in any memorymedium, such as RAM or ROM, and machine code stored on other devices(such as floppy disks, flash memory, or a CDROM, for example). Softwarecan include source or object code, for example. In addition, softwareencompasses any set of instructions capable of being executed in aclient machine or server.

Furthermore, embodiments of the present disclosure can take the form ofa computer program product accessible from a tangible computer-usable orcomputer-readable medium providing program code for use by or inconnection with a computer or any instruction execution system. For thepurposes of this description, a tangible computer-usable orcomputer-readable medium can be any apparatus that can contain, store,communicate, propagate, or transport the program for use by or inconnection with the instruction execution system, apparatus, or device.The medium can be an electronic, magnetic, optical, electromagnetic,infrared, a semiconductor system (or apparatus or device), or apropagation medium.

Data structures are defined organizations of data that may enable anembodiment of the present disclosure. For example, a data structure mayprovide an organization of data, or an organization of executable code.Data signals could be carried across transmission mediums and store andtransport various data structures, and, thus, may be used to transportan embodiment of the present disclosure.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

In one exemplary aspect, the present disclosure is directed to anintegrated circuit (IC) design method. The method includes receiving adesign layout of the IC, the design layout having a first main feature,and adding a negative assist feature to the design layout, wherein thenegative assist feature has a first width, the negative assist featuredivides the first main feature into a second main feature and a thirdmain feature by the first width, and the first width is sub-resolutionin a photolithography process.

In another exemplary aspect, the present disclosure is directed to anintegrated circuit (IC) design method. The method includes receiving adesign layout of the IC, the design layout having a first and a secondmain features, and adding an assist feature to the design layout,wherein the assist feature has a first length and a first width, theassist feature connects the first main feature and the second mainfeature by the first length and the first width is sub-resolution in aphotolithography process.

In another exemplary aspect, the present disclosure is directed to anintegrated circuit (IC) photo mask. The IC photo mask includes a firstmain feature of the IC, a second main feature of the IC and an assistfeature connecting the first and the second main features, wherein theassist feature is a sub-resolution correction feature for correcting foroptical proximity effect.

In another exemplary aspect, the present disclosure is directed to anintegrated circuit (IC) photo mask. The IC photo mask includes a firstfeature and a second feature of the IC, wherein the first and the secondfeatures are spaced a distance from each other, the distance satisfiesmask creation rules and the distance is sub-resolution forphotolithography patterning.

1-9. (canceled)
 10. A method, comprising: receiving a design layout ofan integrated circuit (IC), the design layout having a first mainfeature and a second main feature; and adding an assist feature to thedesign layout, wherein: the assist feature has a first length and afirst width; the assist feature connects the first main feature and thesecond main feature by the first length; and the first width issub-resolution in a photolithography process: and performing an opticalproximity correction (OPC) process to the first and second main featuresto optimize the design layout; and performing a mask rule checking (MRC)process to the optimized design layout, after performing the OPCprocess.
 11. The method of claim 10, wherein the assist feature meets aplurality of mask creation rules.
 12. The method of claim 10, whereinthe photolithography process uses one of: an ultraviolet (UV)lithography process, an extreme ultraviolet (EUV) lithography process,an electron beam lithography process, an X-ray lithography process andan ion beam lithography process.
 13. The method of claim 10, furthercomprising: forming a mask using the IC design layout with the addedassist feature; and exposing an image on a substrate using the mask andthe photolithography process.
 14. (canceled)
 15. The method of claim 10,further comprising: performing a lithography process checking (LPC) tothe design layout to generate a plurality of contours; and adjusting theassist feature and repeating the performing the OPC process and theperforming the MRC process if the plurality of contours do not meet atarget boundary.
 16. The method of claim 15, wherein the target boundaryis defined by an outer boundary of the first main feature and an outerboundary of the second main feature.
 17. The method of claim 15, whereinthe adjusting the assist feature includes one of: changing location ofthe assist feature in the design layout while the assist feature stillconnects the first main feature and the second main feature; increasingthe first width; and decreasing the first width.
 18. An integratedcircuit (IC) photo mask, comprising: a first main feature of the IC; asecond main feature of the IC; and an assist feature connecting thefirst and the second main features, the assist feature being orthogonalto at least one of the first and the second main features; and whereinthe assist feature is a sub-resolution correction feature for correctingfor optical proximity effect.
 19. The IC photo mask of claim 18, whereinthe first and the second main features are modified by an opticalproximity correction (OPC) process.
 20. The IC photo mask of claim 18,wherein the assist feature meets a plurality of mask creation rules.21-29. (canceled)
 30. A method, comprising: receiving a design layout ofan integrated circuit (IC), the design layout having a first mainfeature and a second main feature; and adding an assist feature to thedesign layout, wherein: the assist feature has a first length and afirst width; the assist feature connects the first main feature and thesecond main feature by the first length, the assist feature beingorthogonal at least one of the first and the second main features; andthe first width is sub-resolution in a photolithography process; andperforming an optical proximity correction (OPC) process to the firstand second main features to optimize the design layout; and performing amask rule checking (MRC) process to the optimized design layout, afterperforming the OPC process.
 31. The method of claim 30, wherein theassist feature meets a plurality of mask creation rules.
 32. The methodof claim 30, wherein the photolithography process uses one of: anultraviolet (UV) lithography process, an extreme ultraviolet (EUV)lithography process, an electron beam lithography process, an X-raylithography process and an ion beam lithography process.
 33. The methodof claim 30, further comprising: forming a mask using the IC designlayout with the added assist feature; and exposing an image on asubstrate using the mask and the photolithography process.
 34. Themethod of claim 30, further comprising: performing a lithography processchecking (LPC) to the design layout to generate a plurality of contours;and adjusting the assist feature and repeating the performing the OPCprocess and the performing the MRC process if the plurality of contoursdo not meet a target boundary.
 35. The method of claim 34, wherein thetarget boundary is defined by an outer boundary of the first mainfeature and an outer boundary of the second main feature.
 36. The methodof claim 34, wherein the adjusting the assist feature includes one of:changing location of the assist feature in the design layout while theassist feature still connects the first main feature and the second mainfeature; increasing the first width; and decreasing the first width.